Role of ions and extracellular protein in leukocyte motility and membrane ruffling.

Ruffling and motility, either directed or random, of polymorphonuclear leukocytes (PMNL) were shown to require a monovalent cation (MC). Na+ and Li+ are most effective. These MC-dependent activities are modulated by nonspecific proteins and peptides and are inhibited by cytochalasin B and by alkylating agents such as TPCK (L-[tosylamide-2-phenyl]ethylchloromethyl ketone) but not by ouabain or colchicine. The modulation by protein, but not the inhibition by TPCK or cytochalasin, is competitively inhibited by hydrophobic chemotactic peptides such as f.met-phe and f.phe-met. These hydrophobic peptides, which activate MC influx, promote motility at low concentrations of Na+ (0.1 mM); however, at higher concentrations of Na+ (1.0 mM) the same concentrations of peptides inhibit motility. This inhibition is the result of excessive Na+ and water influx with resultant cellular swelling. The chemotactic peptides, when present as a concentration gradient, function in chemotaxis by competing with the protein at the leading edge of the cell, with resultant local ion influx and swelling. Hydrolysis of the peptide is not required since protease inhibitors have no specific effect on peptide directed migration, although they do inhibit migration. Since local influx of MC and H2O with resultant hydrolysis of ATP is absolutely required for all motility in these cells, it is likely that local swelling and depolymerization of the actin cytoskeletal system are the primary reversible events in PMNL motility. This local swelling or ruffling apparently results in the pushing of cellular contents into the relaxed swollen submembrane areas of the cell by continued contraction of unswollen areas of the cell.